System for evaluating the condition and performance of a valve and valve operator combination

ABSTRACT

A device for measuring and indicating the forces on a valve stem over at least a portion of the valve strokes is comprised of a strain sensor secured to the valve yoke for sensing strains experienced by the valve yoke. The sensed strains are proportional to the forces on the valve yoke and are equal but opposite to the forces on the valve stem. The strain sensor generates electrical signals proportional to the forces on the valve stem. In one embodiment, a second strain sensor is secured to the valve operator for sensing strains experiences by the valve operator and for generating proportional electrical signals. A display, electrically connected to the strain sensors, is provided for receiving the generated electrical signals and for indicating the forces on the valve stem and the forces on the valve operator. A system for evaluating the performance of a valve and valve operator also utilizes the yoke strain sensor in combination with the operator strain sensor and with other sensors, including a valve stem motion sensor, a spring pack motion sensor, a motor current sensor and, possibly, a stem strain sensor, as well as an indicator of the condition of torque and limit switches. In another embodiment, a vibration sensor is secured to the valve operator for sensing vibrations occurring within the valve and/or the valve operator and for generating proportional electrical signals which are displayed in conjunction with other signals for evaluation of valve and valve operator performance.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of copending application Ser. No. 087,541filed Aug. 20, 1987 now U.S. Pat. No. 4,805,451.

BACKGROUND OF THE INVENTION

The present invention relates generally to a system for monitoring andevaluating the condition and performance of a valve and valve operatorcombination and, more particularly, to such a system which employs meansfor sensing strains, experienced by the valve yoke in performing suchevaluation and monitoring.

Numerous prior art systems have been developed for the evaluation ofvalve and valve operator systems, particularly systems which are motoror otherwise power driven and are operated from a remote location. Suchvalves are common in the utility industry and are sometimes used for theprotection of power equipment, as well as for the protection of thegeneral public from the release of hazardous materials, either directlyor indirectly. One such system is disclosed in U.S. Pat. No. 4,542,649,the disclosure of which is incorporated herein by reference.

The background section of the aforementioned patent describes in detailthe problems of the prior art and the need for an improved method formonitoring and evaluating the condition and performance of a valve andvalve operator combination, as well as the need for diagnosingparticular operational problems. Typically, such prior art systemscorrelate valve stem load or forces to the displacement of a spring packby backseating the valve stem against a calibrated load cell whilerecording the displacement of the spring pack resulting from spring packcompression by utilizing a displacement sensor. The resultingcalibration is then used to infer stem loads, seating and backseatingforces as a result of spring pack displacement alone.

The problem with the above-described and other prior art systems is thatthe spring packs typically utilized in conjunction with valve operatorshave substantial initial compression, requiring that the force on thevalve stem build up to a significant predetermined level before thespring pack begins to compress beyond the initial compression and todisplace. This feature of the spring pack leaves a large dead zonewithin which no valve stem force measurement can be made.

In addition, there may be spacing or clearance between the spring packand the spring pack cavity which allows the spring pack to displace theamount of the clearance in response to a minimum or no correspondingforce being imposed on the valve stem. Such clearance adds additionalerror to such prior art systems. Even if the spring pack was tightlyplaced within the spring pack cavity with no such clearance, and even ifthere was no initial compression on the spring pack, the compression ofthe spring pack tends to be non-linear with respect to the forcesencountered by the valve stem. Therefore, spring pack displacement couldnot provide an accurate indication of valve stem forces over the entirerange of spring pack displacement.

Furthermore, it is not uncommon for grease or other lubricants to buildup within the spring pack, possibly filling the entire spring packcavity. Such a buildup of grease or other lubricants can greatly limitspring pack compression, even under the application of very large valvestem forces and, therefore, spring pack displacement would notaccurately reflect valve stem forces. Finally, friction forces on thegears within the valve operator could also cause the spring pack tocompress, even though no forces are actually being placed upon the valvestem. In short, because of the problems of such prior art systems, animproved means for providing a more accurate and precise measure ofvalve stem forces is needed. It is also necessary to provide such ameasurement method utilizing indirect measurement techniques since thevalve stem itself is generally not accessible over the entire valvestroke, therefore making direct measurement difficult and infeasible.

The present invention overcomes the problems of the prior art systems bymeasuring valve stem forces utilizing sensor means secured to the valveyoke. The invention operates on the premise that the forces on the valvestem are opposed by equal and opposite forces in the valve yoke and thatthe measurement of yoke deflection or strain results in a proportionalindicator of the valve stem forces. Unlike the methods employed by theprior art, such a yoke strain measurement provides a linear measure ofvalve stem forces from zero force upwardly which is unaffected by all ofthe above-discussed spring pack anomalies.

The present invention also provides a system for evaluating thecondition and performance of the valve and the valve operator, and foridentifying malfunctions or other problems in either the valve or valveoperator, utilizing the valve stem force measurement (obtained fromvalve yoke strain measurements) in conjunction with other measurements,including valve stem motion, motor current, spring pack motion andtorque and limit switch indications. In addition to diagnosing currentvalve and valve operator problems, the present invention provides amethod for trending changes in overall valve and valve operatorconditions in order to predict future valve or valve operator problems.

SUMMARY OF THE INVENTION

Briefly stated, the present invention comprises a device for measuringand indicating the forces on a valve stem and on a valve operator overat least a portion of the valve stroke. The device comprises firststrain sensor means secured to the valve yoke for sensing strainsexperienced by the valve yoke. The sensed strains are proportional tothe forces on the valve yoke and are equal and opposite to the forces onthe valve stem. The first strain sensor means also generates electricalsignals proportional to the forces on the valve stem. Second strainsensor means are secured to the valve operator for sensing strainsexperienced by the valve operator and for generating electrical signalsproportional to the forces on the valve operator. Display means,electrically connected to the first and second strain sensor means, areprovided for receiving the electrical signals and for indicating theforces on the valve stem and valve operator. The present inventionfurther comprises a system for evaluating the condition and performanceof a valve and valve operator combination utilizing the first and secondstrain sensor means and one or more of a plurality of other sensormeans, including valve stem motion sensor means, spring pack motionsensor means, motor current sensor means, and torque and limit switchindicating means.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description,will be better understood when read in conjunction with the appendeddrawings. For the purpose of illustrating the invention, there is shownin the drawings several embodiments which are presently preferred, itbeing understood, however, that this invention is not limited to theprecise arrangements and instrumentalities shown. In the drawings:

FIG. 1 is an elevational view of a motor operated gate valve shownpartially in section and partially broken away, with the gate partiallyopen and with a first strain sensor means secured to the yoke inaccordance with the present invention;

FIG. 2 is a similar elevational view of the motor operated valve of FIG.1 with the gate in the seated position;

FIG. 3 is a similar elevational view of the motor operated valve of FIG.1 with the gate in the open position;

FIG. 4a is a greatly enlarged perspective view of a preferred embodimentof a tensile strain member employed in the strain sensor means shown inFIG. 1;

FIG. 4b is a side elevational view of the tensile strain member of FIG.4a;

FIG. 4c is a schematic diagram of a preferred strain gage bridge circuitfor use in conjunction with the tensile strain member of FIG. 4a;

FIG. 5 is an enlarged elevational view, partially broken away, of thestrain sensor means of FIG. 1;

FIG. 6 is an enlarged perspective view of the strain sensor means ofFIG. 1;

FIG. 7a is an enlarged sectional view of a valve stem motion sensormeans of the type shown in FIG. 1;

FIG. 7b is a schematic representation of the electrical circuitry of thevalve stem motion sensor means of FIG. 7a;

FIG. 8 is a schematic bock diagram of a preferred system for evaluatingvalve and valve operator condition and performance in accordance withthe present invention;

FIGS. 9a-9k are a flow diagram of a preferred embodiment of a computerprogram for the present invention; and

FIG. 10 is a perspective view of the motor operated gate valve of FIG. 1with a second strain sensor means and an accelerometer secured to thevalve operator.

DESCRIPTION OF PREFERRED EMBODIMENT

Referring now in greater detail to the drawings, in which like numeralsindicate like elements throughout, there is shown in FIG. 1 anelevational view, partially broken away and partially in section, of amotor operated gate valve combination 10. The motor operated gate valve10 is a type which is generally well known in the art and iscommercially available from a variety of sources. The motor operatedgate valve 10 includes a valve member 12 and a valve operator 14 whichare connected together by a valve yoke 16. The valve member or valve 12includes a movable valve gate 18, a fixed valve seat 20 and a fixedvalve backseat 22. The valve gate 18 is movable between a "seated"position in which it engages the valve seat 20 (see FIG. 2), therebyclosing the valve 12 and a "backseated" position in which it engages thevalve backseat 22 (see FIG. 3), thereby fully opening the valve 12. Asshown in FIG. 1, the valve gate 18 is in an intermediate position partway between the seated and backseated positions.

The valve gate 18 moves between the seated and backseated positions bythe action of a valve stem 24, one end of which is secured to the valvegate 18. The valve stem 24 extends through suitable openings in thevalve 12 and valve yoke 16 with the other end extending into the valveoperator 14, as shown.

The valve operator 14 is comprised of a motor 26 which in the presentembodiment is shown as being an electric motor. The output shaft of themotor 26 is connected through suitable reduction gears 28 to acombination worm and worm gear, shown collectively as 30. The worm gearincludes an internal threaded opening (not shown) which serves as a stemnut to engage threading on the upper end of the valve stem 24. Rotationof the drive shaft of the motor 26 results in rotation of the worm andworm gear 30 and corresponding vertical movement of the valve stem 24.The direction of movement of the valve stem 24 depends upon thedirection of movement of the output shaft of the motor 26. Of course,the vertical movement of the valve stem 24 results in correspondingmovement of the valve gate 18.

The distal (rightmost) end of the worm is connected to a spring pack 32in a manner well known in the art. A separate small gear 34 is alsoconnected to the worm by way of the spring pack 32. The gear 34, inturn, is connected to a torque switch (not shown) having two sets ofelectrical contacts for deactivating the motor 26 when the gear 34 isturned due to a displacement of the spring pack 32. One set of contactscalled the open torque switch opens to deactivate the motor 26 forspring pack motion in one direction corresponding to impeded stem motionin the valve opening direction and the other set of contacts called theclose torque switch opens to deactivate the motor 26 for spring packmotion in the other direction corresponding to impeded stem motion inthe valve closing direction. Also associated with the valve operator 14is a manual actuator 36 to permit the valve operator 14 to be operatedindependently of the motor 26.

The structure thus far described is typical of that of a motor operatedgate valve of the type with which the present invention may be employed.It will be appreciated by those skilled in the art that the motoroperated gate valve 10 is merely an illustrative example of one valvewith which the present invention may be employed and that the presentinvention may alternatively be employed with any other type of valve(such as a globe valve) or with any other type of valve operator, suchas a pneumatic or hydraulic valve operator (not shown). The presentinvention may also be employed with a butterfly valve to sense stemtorque. Further details of the structure and operation of the motoroperated gate valve 10 will be presented only insofar as is necessaryfor an understanding of the structure and operation of the presentinvention as described below.

A first strain sensor means or yoke strain sensor 38 is secured to thevalve yoke 16 for sensing strains experienced by the valve yoke 16. Inthe present embodiment, the yoke strain sensor 38 is comprised of atensile strain member 40 which is best seen in FIGS. 4a and 4b. Thetensile strain member 40, in the present embodiment, is a generally flatelongated beam 42 having first and second elongated surfaces 44 and 46(see FIG. 4b) on opposite sides. In the present embodiment, the beam 42is in the shape of an "I" beam in a top plan view. However, the presentinvention is not limited to a particular shape for the beam 42. The beam42 is preferably formed of a high tensile strength metallic materialsuch as beryllium copper due to its spring-like properties. However, thebeam 42 could be formed of any other suitable material. Mounting holes48, in the present embodiment four such mounting holes, extend throughthe beam 42 to facilitate mounting the beam 42 onto the valve yoke 16 ina manner which will hereinafter become apparent.

At least one strain gage is secured or bonded to the tensile strainmember 40. In the present embodiment, there are four such strain gages,T1, P1, T2 and P2, secured to the tensile strain member 40. The straingages are of a type well known in the art and generally commerciallyavailable. Two of the strain gages, T1 and T2, are longitudinallyoriented with respect to the tensile strain member to experience andindicate longitudinal or tensile strain. The other strain gages, P1 andP2, are transversely oriented with respect to the tensile strain member40 to experience transverse or Poisson strain. In general, Poissonstrain is opposite in sense to tensile, and is equal to about one-thirdof the magnitude of tensile strain. The use of multiple strain gageshaving different orientation is superior to a single strain gage due toincreased sensitivity and inherent thermal compensation. In the presentembodiment, one of the longitudinally oriented strain gages, T1, and oneof the transversely oriented strain gages, P1, are secured to the firstsurface 44 of the tensile strain member 40 and the other two straingages T2 and P2 are secured to the second surface 46 of the tensilestrain member 40. The strain gages, T1, P1, T2 and P2 are secured orbonded to the tensile strain member 40 utilizing suitable epoxy or otheradhesives, or in any other manner known in the art. While, in thepresent embodiment, the strain gages are secured to the tensile strainmember 40 in the specific manner, locations and orientations shown anddescribed, they could be secured to the tensile strain member 40 in someother manner, location and/or orientation.

The yoke strain sensor 30 further includes a four active arm strain gagebridge circuit 50 as schematically illustrated in FIG. 4c. The straingage bridge circuit 50 is made up of the electrically connected straingages, T1, P1, T2 and P2, utilizing suitable electrical conductors,preferably insulated wires or leads 52. Strain gage bridge circuits ofthe type illustrated in FIG. 4c are generally well known in the art and,therefore, need not be described in detail. Suffice it to say that uponthe application of a D.C. excitation voltage V_(IN) to the inputterminals of the strain gage bridge circuit 50, electrical signals,proportional to the forces on the valve yoke 16 are generated by thebridge circuit 50 and appear on the output terminals as a D.C. voltageV_(OUT). The magnitude of the output voltage V_(OUT) is proportional tothe magnitude of the applied tensile strain which occurs when thetensile strain member 40 is placed in tension, as will hereinafterbecome apparent.

As best seen in FIG. 5, the tensile strain member 40 is secured on eachlongitudinal end to mounting means, in the present embodiment comprisingmounting blocks 54 and slightly smaller clamping blocks 56. The clampingblocks 56 are secured to the mounting blocks 54 utilizing suitably sizedscrews or bolts 58 which extend through the holes 48 in the tensilestrain member 40 and into suitable taped openings in the mounting blocks54. After the mounting blocks 54 and clamping blocks 56 have beensecured to the tensile strain member 40, the entire assembly isencapsulated with a flexible, stretchable material, such as rubber 60,to provide environmental protection for tensile strain member 40 and thevarious strain gages. The rubber material 60 provides the requiredprotection without appreciably altering the spring constant of theassembly. As best seen in FIG. 5, the distal ends of the mounting blocks54 ar not encapsulated in the rubber material 60 in order to permit theassembly to be secured to the valve yoke 16, as will hereinafter bedescribed. Of course, the leads 52 extend outwardly from theencapsulating rubber 60.

The yoke strain sensor 38 is secured to the valve yoke 16 by a pair ofmounting posts 62 and 64 (see FIG. 6). Before installing the yoke strainsensor 38, the mounting posts 62 and 64 are secured to the valve yoke 16in a predetermined, precisely spaced relationship to create apredetermined initial tension in the yoke strain sensor 38 when it isinstalled. The predetermined initial yoke strain sensor tension iscreated to facilitate the sensing of compressive strains in the valveyoke 16 due to tensile forces on the valve stem 24 in addition to thesensing of tensile strain in the valve yoke 16 due to compressive forcesin the valve stem 24. The mounting posts 62 and 64 may be secured to thevalve yoke 16 utilizing soldering, brazing, welding, epoxy or some otherkind of adhesive, or in any other manner known in the art.

In order to establish the precise predetermined spacing required betweenthe mounting posts 62 and 64, a spacer block (not shown) may bepositioned between the mounting posts. Once the mounting posts 62 and 64are secured to the valve yoke 16 with the predetermined spacing, thespacer block is removed and the yoke strain sensor 38 is installedbetween the mounting posts 62 and 64, as best seen in FIG. 6. Aplurality of securing means, such as screws 68, are employed to securethe exposed portions of the mounting blocks 54 to the mounting posts 62and 64. The spacer block (not shown) used in installing the mountingposts 62 and 64 is longer than the yoke strain sensor 38, so that whenthe mounting screws 68 are tightened to pull the mounting blocks 54 intoengagement with the mounting posts 62 and 64, the desired predeterminedstrain is placed upon the tensile strain member 40. A suitably sizednotch 70 is provided in mounting post 64 to accommodate the leads 52 ofthe yoke strain sensor 38.

With the yoke strain sensor 38 secured to the valve yoke 16, between themounting posts 62 and 64, as shown and described, the strain experiencedby the valve yoke 16 is amplified as applied to the yoke strain sensor38. The amount of amplification is equal to the ratio of the effectivemounting distance between the mounting posts 62 and 64 and the freelength of the tensile strain member 40 inside the mounting and clampingblocks 54 and 56, respectively. The amplification factor effectivelyincreases the sensitivity of the yoke strain sensor 38 with respect tothe sensing and indication of strain experienced by the valve yoke 16.

At least one display means is electrically connected to the yoke strainsensor means 38 for receiving the electrically generated signals and forindicating the forces on the valve stem 24. In the present embodiment,as shown in FIG. 1, the display means is comprised of a voltagesensitive meter 72 electrically connected by the leads 52 to the yokestrain sensor 38. The meter 72 indicates both the output voltage and thepolarity of the voltage generated by the yoke strain sensor 38, asdetermined from the strain gage bridge circuit 50 described above. Asindicated above, the magnitude of the voltage is proportional to themagnitude of the forces on the valve stem 24. The polarity of thevoltage indicates whether the forces on the valve stem 24 arecompressive or tensile. Alternatively, the display means could comprisea computer system 74 (shown diagrammatically in FIG. 1 as a computerterminal or CRT screen), further details of which will hereinafterbecome apparent.

Referring now to FIGS. 1, 2 and 3, a brief description of thefunctioning of the yoke strain sensor 38 will be presented.

When the valve 12 is to be closed, electrical power is supplied to themotor 26 which operates through the reduction gears 28 to drive the wormand worm gear 30 to rotate in a first direction. Rotation of the wormand worm gear 30 and the internal stem nut (not shown) moves the valvestem 24 downwardly, thereby moving the valve gate 18 toward the valveseat 20. When the valve gate 18 engages the valve seat 20 (see FIG. 2),the downward motion of the valve stem 24 substantially stops, in turncausing the stem nut and worm gear to also stop. The worm, whichcontinues to rotate because of the driving force of the motor 26 andreduction gears 28, is forced to move axially (toward the right whenviewing FIG. 2), pushing the spring pack 32 toward the right (whenviewing FIG. 2) and compressing the spring pack 32 to the position shownin FIG. 2. The rightward movement and compression of the spring pack 32results in rotation of the gear 34 which, in turn, opens the torqueswitch (not shown) to cut off the power to stop the motor 26. The delayin time which occurs between the valve gate 18 engaging the valve seat20 and the motor 26 being stopped, although relatively brief, stillresults in an increase in the compressive forces on the valve stem 24,indicated by arrows 76, which continue to build until the motor 26 isactually stopped. The valve stem compressor forces 76 cause equal andopposite tensile forces, shown by arrows 78, in the valve yoke 16, andthe resulting yoke deflection or strain is sensed by the yoke strainsensor 38, as previously described.

In opening the valve 12, the motor 26 drives the worm and worm gear 30in the opposite direction, resulting in the valve gate 18 movingupwardly away from the valve seat 20 and toward the valve backseat 22.When the valve gate 18 reaches the backseat 22, as shown in FIG. 3, themotion of the valve stem 24 again substantially stops, causing the stemnut and worm gear to stop. Again, since the motor 26 continues tooperate, the worm continues to rotate and, therefore, must move axially.However, in this case, the axial movement of the worm is pulling against(toward the left when viewing FIG. 3) but is still compressing thespring pack 32, to the position as shown in FIG. 3. As the spring pack32 is compressed, the gear 34 rotates to open the torque switch (notshown) to cut off the power to stop the motor 26. When the valve gate 18is fully engaged against the backseat 22, the delay in stopping themotor 26 results in an increase in the tensile forces in the valve stem24. The valve stem tensile forces, shown as arrows 80, cause equal andopposite compressive forces, shown as arrows 82, in the valve yoke 16.The resulting deflection or strain of the valve yoke 16 is sensed by theyoke strain sensor 38. As previously discussed, the polarity of thesignal generated by the yoke strain sensor 38 is the opposite of thatgenerated upon closing of the valve 12.

As best shown in FIG. 1, the portion of the valve 12 through which thevalve stem 24 extends, is packed with a suitable packing material 84 ofa type well known and conventionally used in the art. The purpose of thepacking material 84 is to prevent fluid passing through the valve 12from inadvertently leaking into the valve yoke 16. The packing material84 places some forces upon the valve stem 24. If excessive packingforces are present, such forces are indicated during the closing of thevalve 12 as additional compression in the valve stem 24 and, therefore,additional tension in the valve yoke 16 prior to seating of the valvegate 18. Correspondingly, when the valve 12 is opening, such packingforces will be indicated as an additional tension in the valve stem 24and corresponding additional compression in the valve yoke 16 prior tobackseating of the valve gate 18. In either situation, such additionalforces are sensed by the yoke strain sensor 38.

The strains on the valve yoke 16 accurately reflect all of the reactiveforces experienced by the valve yoke 16 and, correspondingly, the valvestem 24. These strains are completely independent of all otherpotentially misleading effects to provide an accurate and relativelyprecise measurement. However, it is desirable to calibrate the yokestrain sensor 38 before making such measurements. Several alternativemethods may be employed for such calibration. The yoke strain sensor 38may be calibrated by measuring its output voltage while mechanically orhydraulically imparting a known or accurately measured axial force orload to the valve yoke 16 after placing the valve 12 in a condition inwhich the imposed load is not shared by the valve stem 24, i.e., beforethe valve 12 and valve operator 14 are assembled together or afterassembly in the valve stem thread clearance direction. Alternatively,the yoke strain sensor 38 may be calibrated by measuring the outputvoltage while mechanically or hydraulically imparting a known ormeasured axial reactive force or load to the valve stem 24 of a fullyassembled valve. Preferably, the forces or load are applied to the stemduring important portions of the valve stroke, such as a fully openedvalve 12 or a fully closed valve 12, in which the applied load isexperienced in total by both the valve stem 24 and the valve yoke 16.

While the foregoing described methods are acceptable for calibrating theyoke strain sensor 38, they are not always feasible, particularly in thecase of a valve 12 which has been previously installed and isoperational. The preferred calibration method is to temporarily secure asecond strain sensor means directly to the valve stem 24. The secondstrain sensor means or stem strain sensor 86 is employed for directlysensing strains experienced by the valve stem 24 and for generatingelectrical signals proportional thereto. The valve stem strain sensor 86may be any type of strain sensor well known in the art, for example, adiametral strain sensor, a circumferential strain sensor, a longitudinalstrain sensor, or any other type of strain sensor for measuring the stemstrains that result when the valve 12 is operated in a large loadgradient region of its stroke, such as seating, unseating, backseating,etc. In this manner, calibration is accomplished by applying any forceor load (whether known or not) to the valve stem 24 and establishing thesimple relationship between the stem strains measured directly by thevalve stem strain sensor 86 and the forces measured by the yoke strainsensor 38.

In many operating conditions, it will be necessary to remove the valvestem strain sensor 86 from the valve stem 24 to permit full operation ofthe valve 12, particularly if the valve stroke is too great to allow itto remain in place without damaging the valve stem strain sensor 86 orotherwise affecting valve operation. However, the calibrated yoke strainsensor 38 may remain permanently attached to the valve yoke 16 toprovide signals proportional to the forces on the valve stem 24 any timethe valve 12 is operated.

As previously described, a relatively inexpensive meter 72 may beemployed in conjunction with the yoke strain sensor 38 to provide anoperator with sufficient information concerning the forces on the valvestem 24 to permit the operator to control the seating or the forcesapplied during manual operation. Similarly, an operator, at a remotelocation, opening or closing the valve utilizing the valve operator 14,is provided with information for controlling the seating or forcesapplied to the valve stem 24 during operation.

The calibrated yoke strain sensor 38, in conjunction with the meter 72or computer terminal or CRT screen 74, is sufficient to permit theoperator to diagnose many problems which could occur during operation ofthe valve 12. Examples of the problems which could be diagnosed includeexcessive or insufficient valve gate seating forces; excessive orinsufficient forces for unseating the valve gate 18; excessive orinsufficient packing forces imposed on the valve stem 14 by the packingmaterial 84; a tapered stem condition which is determined by asymmetrical increasing or decreasing of packing forces on opening versusclosing; offset gears or gears having damaged or missing teeth which arediscernible as either a sine wave or spiked modulation of forcemagnitude at the gear rotational rate and a damaged seat conditiondiscernible from an unusual or changing pattern in the seating orunseating valve stem force signature.

As will hereinafter be described, by combining the informationpertaining to the forces on the valve stem 24 obtained by the yokestrain sensor 38 with information obtained from additional sensors(hereinafter described), a system is developed for evaluating thecondition and performance of both the valve 12 and the valve operator 14to diagnose many additional problems which may occur.

Referring now to FIGS. 7a and 7b, there is shown a device for detectingaxial motion of a valve stem 24 which has been installed within and issurrounded by a valve yoke 16 so that the ends of the valve stem 24 areunavailable for the installation of prewound coil. The axial motiondetection device or valve stem motion sensor, shown generally as 90, iscomprised of a predetermined length of generally flat, multiconductorcable 92, sometimes referred to as "ribbon" cable, having a firstconnector component 94 secured to one end and a second connectorcomponent 96 secured to the other end. The first connector component 94has a plurality of individual electrical contacts (not shown), thenumber of contacts being at least two greater than the number ofconductors in the ribbon cable 92. The second connector component 96similarly has a plurality of electrical contacts, the number of contactsbeing at least two greater than the number of conductors of the ribboncable 92. The two connector components 94 and 96 are adapted to beinterconnected, as shown in FIG. 7a, with the ribbon cable 92surrounding the valve stem 24. The length of the ribbon cable 92 isselected to permit the ribbon cable 92 to completely surround the valvestem 24 in close proximity without being in direct contact with thevalve stem 24 in a manner which would in any way impair axial movementof the valve stem 24.

The conductors of the ribbon cable 92 are electrically connected to thecontacts of the first and second connector components 94 and 96 in sucha manner that when the connector components 94 and 96 are coupledtogether, as shown in FIG. 7a, the ribbon cable 92 forms two generallyparallel but electrically independent coils, each of the coils extendingaround the valve stem 24, as shown schematically in FIG. 7b. One way ofconnecting the conductors of the ribbon cable 92 to the first and secondconnector components 94 and 96 is to offset the connectors by twocontacts so that the first connector component 94 has two open or unusedcontacts, A and B on one end, and the second connector components 96 hastwo open or unused contacts, A and B on the other end. In this manner,one complete coil is formed between the B contacts and the othercomplete coil is formed between the A contacts. Of course, any othersuitable method of connecting the conductors of the ribbon cable 92 toprovide two independent generally parallel coils could alternatively beemployed.

In operation, a current source is electrically connected to both ends ofone of the coils to provide for a flow of current through the one coil.Axial movement of the valve stem 24 through the coils results in avoltage being induced in the other coil in a manner well known in theart. The induced voltage which can be received from the other pair ofunused contacts is proportional to the velocity of the axial movement ofthe valve stem 24 through the coils. The polarity of the induced voltageindicates the direction of axial movement of the valve stem 24 throughthe coils.

The motion detecting device 90, as described, could alternatively beemployed for in situ detection of axial movement of any generallycylindrical member, particularly in a situation in which both ends ofthe member are unavailable for the installation of a prewound coil. Theends of the member may be unavailable because they are already attachedto another structure or because they are otherwise inaccessible. Inemploying the device 90 for in situ detection of axial movement of agenerally cylindrical member, the structure and above-describedoperational features of the device 90 remain the same. However, thelength of the ribbon cable 92 may vary, depending upon the outerdimension of the cylindrical member being surrounded.

The coil within which the voltage is induced is electrically connectedto a suitable display means in a manner well known in the art. Thedisplay means could be a meter, such as meter 72 (FIG. 1).Alternatively, the display means could be a computer system, such ascomputer system 74.

As previously indicated, information concerning the velocity anddirection of movement of the valve stem 24 which is obtained from themotion detecting device 90 can be used in conjunction with theinformation pertaining to the forces on the valve stem 24 obtained bythe yoke strain sensor 38. For example, the information could be used indiagnosing a loose stem nut condition, a motor 26 which has beenimproperly connected and is turning in the wrong direction, changeswhich may occur in lost motion areas, teeth which may be missing fromgears, and inappropriate system clearances.

As indicated above, the yoke strain sensor 38 may be employed as part ofa system for evaluating the condition and performance of a valve andvalve operator combination, such as motor operated gate valve 10. Aschematic block diagram of a preferred embodiment of such a system isshown in FIG. 8, the system being shown generally by reference numeral100. The system 100 receives signals from the yoke strain sensor 38 andthe valve stem motion sensor 90 in the manner as previously described.Similarly, if available, the system 100 receives signals from the valvestem strain sensor 86. Three other means are employed for providingspecialized signals to the system 100. A spring pack sensor means, inthe present embodiment a spring pack motion sensor 102 is secured to thedistal (rightmost when viewing FIG. 1) end of the spring pack 32 fordetecting the motion and direction of movement of the spring pack 32.The spring pack motion sensor 102 generates electrical signals with amagnitude proportional to the velocity of spring pack movement and witha polarity indicative of the direction of spring pack movement. Thespring pack motion sensor 102 is of a type generally well known in theart and commercially available.

Motor current sensor means, in the present embodiment a motor currentsensor 104 secured to at least one of the power lines to the motor 26 isprovided for detecting the flow of current through the motor 26 and forgenerating electrical signals proportional to the motor current. Themotor current sensor 104 is also of a type generally well known in theart and generally commercially available.

Torque and limit switch indicating means, in the present embodiment atorque and limit switch indicator 106 electrically connected to thetorque and limit switches (not shown) associated with the valve andvalve operator 14 is provided for detecting the state of the torque andlimit switches and for generating electrical signals representative ofthe state of the torque and limit and switches.

Vibration measuring means, in the present embodiment, an accelerometer,105 is secured to the valve operator 14 as shown in FIG. 10. Theaccelerometer 105 detects vibrations occurring in the valve operatorwhich may result from various abnormalities in the operation of thegears within the valve operator and/or vibration resulting from abnormaloperation of the spring pack, as well as normal valve and valve operatorvibrations. The accelerometer 105 is of a type generally well known inthe art and generally commercially available. The accelerometer 105generates electrical signals proportional to the sensed vibrations in amanner which is also generally well known in the art. The generatedelectrical signals are fed along line 107 to the display means (notshown on FIG. 10).

The evaluation system 100 further comprises a series of signalconditioners 108, associated with the various sensors and indicators forfiltering, amplifying and otherwise conditioning the various receivedelectrical signals to predetermined levels suitable for furtherprocessing. The signal conditioners 108 are of a type which aregenerally well known in the art and commercially available.

The system 100 also includes a multiplexer and digitizer 110 which iselectrically connected to each of the signal conditioners 108. Themultiplexer and digitizer 110 receives the conditioned analog electricalsignals from the signal conditioners 108, multiplexes the signals,preferably on a time division basis, and digitizes or converts theanalog signals to digital form. The multiplexer and digitizer is of atype generally well known in the art and commercially available.

The system 100 further includes an analysis section comprised of adigital computer 112 and associated peripheral equipment, including amemory, in the present embodiment disk storage 114, a hard copy outputmeans, in the present embodiment an XY or similar type of plotter 116and an input/output device, in the present embodiment a CRT display 118which may include a keyboard (not shown).

The computer 112 receives the multiplexed digital signals representativeof the various sensors and indicators from the multiplexer and digitizer110. The computer 112, operating in accordance with a previously storedprogram, stores the digital signals or samples representative of thevarious forces, motions, etc. concerning the valve 12 and valve operator14 to establish a digital record for each force, motion, etc. forpredetermined time periods. The computer 112 then compares various onesof the digital records with others of the digital records to moreclearly define valve and valve operator operation. In addition, thecomputer 112 compares various of the digital records with previouslystored reference digital records of the corresponding force, motion,etc. expected to be experienced during normal operation and indicatesdeviations resulting from the comparison. The computer also compares thedigital records for each force, motion, etc. with previously storeddigital records for the same force, motion, etc. for indicating changesand trends in the force, motion, etc. over time to predict future valveand valve operator operation. Finally, the computer 112 displays thevarious force, motion, etc. digital records in a humanly readable form,either on the plotter 116 or on the CRT screen 118 to permit theoperator to identify disruptions in normal valve operator to valvefunctioning.

The computer 112 may utilize information obtained from the yoke strainsensor 38 in combination with the information obtained from the springpack motion sensor 102 to diagnose a condition of excessive spring packfree load discernible by an already large stem force at the time thespring pack starts to move. The same combination can be employed toindicate a grease-filled or grease-hardened spring pack identifiable bysmall spring pack motion with a large corresponding stem force buildupor excessive spring pack clearance, a condition discernible by springpack motion associated with no corresponding stem force buildup.

Similarly, the computer 112 can utilize the information obtained fromthe yoke strain sensor 38 in combination with the motor current sensor104 to diagnose a condition of excessive gear friction discernible by anincrease in motor current and a corresponding decrease in valve stemforce. Similarly, an offset or damaged gear condition could be diagnosedthrough amplitude or frequency modulation of the motor current at amodulation rate equal to the gear rotation speed.

By combining the information obtained from the yoke strain sensor 38with the information obtained from the torque and limit switch indicator106 (FIG. 8), the computer can diagnose the condition of a misadjustedtorque switch indicated by a seating or backseating valve stem forcewhich is either too large or too small from that normally expected.Similarly, a misadjusted limit switch could be identified if the motoris stopped before the torque switch opens upon valve seating. Thecondition of a misadjusted bypass switch is indicated when the motor isallowed to be stopped by the torque switch on unseating of the valve.

The computer 112 can utilize the information obtained from the yokestrain sensor 38 in combination with the information obtained from theaccelerometer 105 for diagnosing gear abnormality conditions and springpack abnormality conditions. Both are determined by demodulating theaccelerometer signal at a frequency generally corresponding to the wormgear mesh frequency. The modulated worm gear mesh frequency signalcontains information about all gear abnormalities and spring packfunctions. For example, an offset worm gear would result in a modulationof the worm gear mesh frequency at the rate at which the worm gearrotates. Correspondingly, the beginning of spring pack movementcorresponds to a discontinuity in worm gear mesh frequency in a mannerso that the force measured by the yoke strain sensor 38 at thecorresponding time indicates the degree of spring pack precompression.

A computer program adapted to permit the computer 112 to perform thevarious comparison and indicating functions necessary for evaluating thecondition and performance of the valve 12 and valve operator 14combination is well within the skill of a person skilled in theprogramming arts and, therefore, need not be presented herein. However,FIGS. 9a through 9k provide a schematic flow diagram of a preferredembodiment of the principal features of such a program. A detaileddiscussion of the flow diagrams shown in FIGS. 9a through 9k is notbelieved to be necessary for a complete understanding of the presentinvention and, therefore, will not be presented. However, specificexamples are set fort below.

The computer 112 receives and stores digital samples representative ofvalve stem forces for predetermined time periods to establish a valvestem force digital record. The computer then compares the valve stemforce digital record with a previously stored valve stem force referencerecord of the forces expected to be experienced by the valve stem duringnormal operation. The computer then provides an indication of deviationsresulting from the comparison and, if the deviations fall outside ofpredetermined limits, the computer alerts the operator. Similarly, thecomputer compares the valve stem force digital record withcorresponding, previously stored valve stem force digital records forindicating changes and trends over time with respect to the forces onthe valve stem. Again, if the changes or trends fall outside ofpredetermined limits, the computer alerts the operator.

As previously described, the computer 112 also displays informationpertaining to valve stem strain (if applicable), motor current, valvestem motion, spring pack motion and the state of the torque and limitswitches. Similarly, each of the various informations is compared by thecomputer to reference information relating to normal valve functioningand to previously stored information to provide trends. In addition, theinformation from the yoke strain sensor 38 is compared to theinformation from each of the other sensors and the torque and limitswitch indicator information for diagnosis of specific problems, asdiscussed in detail above. Each of the various displays and comparisonsis made on a continuing or periodic basis during valve operation. Inthis manner, the computer 112 keeps the operator continuously informedconcerning the structural condition and performance of the entire valveand valve operator combination, as well as providing the operator withdiagnostic information concerning particular problems occurring at anygiven time or problems which may occur at some time in the future basedupon trends.

FIG. 10 illustrates an alternate embodiment of the present invention. Inthe embodiment shown in FIG. 10, which is essentially the same as theabove-described embodiments, a second strain sensor means 200 is securedto an outer surface of the valve operator 14. Preferably, the secondstrain sensor means or operator strain sensor 200 is structurally thesame as the yoke strain sensor 38, which has previously been describedin detail and is illustrated in FIGS. 4a through 4c. However, some othertype of strain sensor means could alternatively be employed. As with theyoke strain sensor 38, the operator strain sensor 200 is secured to theouter surface of the valve operator 14 utilizing mounting means, in thepresent embodiment comprising a pair of mounting posts 202 which aresubstantially the same as mounting posts 62 and 64 (see FIG. 6) employedfor mounting the yoke strain sensor 38 on the valve yoke 16. Theoperator strain sensor 200 is not employed for the measurement ofcompressive strains in the valve operator 14. Accordingly, it is notnecessary to position the mounting posts 62 in a precisely spacedrelationship to create a predetermined initial tension on the operatorstrain sensor 200. Instead, the mounting posts 202 are secured to thevalve operator 14 so that the operator strain sensor 200 experiences noinitial tension or compression although an initial tension could beapplied, if desired. The mounting posts 202 may be secured to the valveoperator 14 utilizing soldering, brazing, welding, epoxy, or some otherkind of adhesive, or in any other manner known in the art. The operatorstrain sensor 200 may be secured to the mounting posts 202 utilizing aplurality of screws (not shown), wax (not shown) or any other suitablepermanent or temporary securing means. Suitable electrical leads 204extend outwardly from the operator strain sensor 200 to a display means(not shown in FIG. 10). The display means may be any of the varioustypes of display means described above.

The operator strain sensor 200 is provided for sensing tensile forcesapplied to the valve operator 14. Such tensile forces are generallyexperienced by the valve operator 14 upon seating of the valve gate 18against the valve seat 20 (FIG. 1) during valve closing and, duringvalve opening, when artificially restricting the opening movement of thevalve stem 24 at the top of the valve operator to verify open torqueswitch setting. In a valve going through a normal closing stroke, thetensile forces experienced by the valve yoke 16 and the yoke strainsensor 38 are identical to the tensile strain forces experienced by theoperator 14 housing and the operator strain sensor 200. Therefore, theoperator strain sensor 200 may be calibrated in the same manner as abovedescribed with respect to the yoke strain sensor 38. During a restrictedopening, restricted at the top of the valve operator as described above,the calibrated signal from the operator strain sensor 200 can be used incombination with the signal indicating when the open torque switch opensto determine whether the open torque switch is opening at the properforce level. With a valve undergoing a normal opening stroke, althoughcompressive forces are experienced by the valve yoke 16, no tensile orcompressive forces are experienced by the operator housing or theoperator strain sensor 200. Thus, the signal generated by the operatorstrain sensor 200 indicates a clear transition point as the stemtransitions from compression to tension. The corresponding point on theyoke strain sensor output signal is thus a known zero force point on thevalve stem. It will be recognized by those skilled in the art that thesignals generated by the operator strain sensor 200 could alternativelybe employed in conjunction with other diagnostic signals of the typedescribed above, or of any other type, for the purpose of providinginformation concerning the functioning of the valve and valve operator.

From the foregoing description, it can be seen that the presentinvention comprises a system for evaluating the condition andperformance of a valve and valve operator combination utilizing a strainsensor means secured to the valve yoke for sensing and indicating valvestem forces. It will be appreciated by those skilled in the art thatchanges could be made to the embodiment described above withoutdeparting from the broad inventive concept thereof. It is understood,therefore, that this invention is not limited to the particularembodiment disclosed, but it is intended to cover all modificationswhich are within the scope and spirit of the invention as defined by theappended claims.

I claim:
 1. A device for measuring and indicating the forces on a valvestem of a valve having an operator within an operator housing, over atleast a portion of the valve stroke, the device comprising:first strainsensor means secured to a valve yoke and substantially parallel to thevalve stem for sensing strains experienced by the valve yoke which areproportional to the forces on the valve yoke and are equal and oppositeto the forces on the valve stem, the first strain sensor means forgenerating first electrical signals proportional to the forces on thevalve stem; second strain sensor means secured to the valve operatorhousing for sensing strains experienced by the operator housing, thesecond strain sensor means for generating second electrical signalsproportional to forces on the operator housing; and display meanselectrically connected to the first and second strain sensor means forreceiving the first and second electrical signals and for indicating theforces on the valve stem and the operator housing.
 2. The device asrecited in claim 1 wherein the first and second strain sensor means areeach comprised of:a tensile strain member; and a strain gage bridgecircuit connected to the display means, and including at least onestrain gage secured to the tensile strain member.
 3. The device asrecited in claim 2 wherein the first and second strain sensor means eachfurther comprises four strain gages secured to the tensile strainmember, two of the strain gages being longitudinally oriented withrespect to the member to experience longitudinal strain and two of thestrain gages being transversely oriented with respect to the member toexperience Poisson strain, the four strain gages forming the strain gagebridge circuit.
 4. The device as recited in claim 3 wherein each tensilestrain member is a generally flat elongated beam having first and secondopposite elongated surfaces, two of the strain gages being secured tothe first surface and two of the strain gages being secured to thesecond surface.
 5. The device as recited in claim 4 wherein onelongitudinally oriented strain gage and one transversely oriented straingage is secured to each of said first and second surfaces of each beam.6. A system for evaluating the condition and performance of a valve andvalve operator combination, including a valve, a valve operator, a valvestem extending between the valve operator and the valve, and a valveyoke surrounding the valve stem, the system comprising:first strainsensor means secured to the valve yoke and substantially parallel to thevalve stem for sensing strains experienced by the valve yoke which areproportional to the forces on the valve yoke and are equal and oppositeto the forces on the valve stem, the first strain sensor means also forgenerating electrical signals proportional to the forces on the valvestem; second strain sensor means secured to the valve operator forsensing strains experienced by the valve operator and for generatingelectrical signals proportional to the forces on the valve operator;valve stem motion sensor means for detecting motion and direction ofmovement of the valve stem and for generating electrical signalsproportional to the velocity of valve stem movement, the signals havinga polarity indicative of the direction of valve stem movement; anddisplay means electrically connected to the first and second strainsensor means and to the valve stem motion sensor means for receiving thegenerated electrical signals and for indicating the forces on the valvestem, and on the valve operator and the corresponding valve stemvelocity to permit identification of a disruption in normal valve and/orvalve operator functioning.
 7. A system for evaluating the condition andperformance of a valve and valve operator combination, including avalve, a valve operator containing a motor, gearing, a spring pack andtorque and limit switches, a valve stem extending between the valveoperator and the valve, and a valve yoke surrounding the valve stem, thesystem comprising:first strain sensor means secured to the valve yokeand substantially parallel to the valve stem for sensing strainsexperienced by the valve yoke which are proportional to the forces onthe valve yoke and are equal and opposite to the forces on the valvestem, the first strain sensor means also for generating electricalsignals proportional to the forces on the valve stem; second strainsensor means secured to the valve operator for sensing strainsexperienced by the valve operator and for generating electrical signalsproportional to forces on the valve operator; spring pack motion sensormeans for detecting motion and direction of movement of the spring packand for generating electrical signals proportional to the velocity ofspring pack movement, the signals having a polarity indicative of thedirection of spring pack movement; and display means electricallyconnected to the first and second strain sensor means and to the springpack motion sensor means for receiving the generated electrical signalsand for indicating the forces on the valve stem, and on the valveoperator and the corresponding spring pack velocity to permitidentification of a disruption in normal valve and/or valve operatorfunctioning.
 8. A system for evaluating the condition and performance ofa valve and valve operator combination, including a valve, a valveoperator containing a motor, gearing, a spring pack and torque and limitswitches, a valve stem extending between the valve operator and thevalve, and a valve yoke surrounding the valve stem, the systemcomprising:first strain sensor means secured to the valve yoke andsubstantially parallel to the valve stem for ensing strains experiencedby the valve yoke which are proportional to the forces on the valve yokeand are equal and opposite to the forces on the valve stem, the firststrain sensor means also for generating electrical signals proportionalto the forces on the valve stem; second strain sensor means secured tothe valve operator for sensing strains experienced by the valve operatorand for generating electrical signals proportional to forces on thevalve operator; motor current sensor means for detecting the flow ofcurrent through the motor and for generating electrical signalsproportional to the motor current; and display means electricallyconnected to the first and second strain sensor means and to the motorcurrent sensor means for receiving the generated electrical signals andfor indicating the forces on the valve stem, and on the valve operatorand the corresponding motor current to permit identification of adisruption in normal valve and/or valve operator functioning.
 9. Asystem for evaluating the condition and performance of a valve and valveoperator combination, including a valve, a valve operator containing amotor, gearing, a spring pack and torque and limit switches, a valvestem extending between the valve operator and the valve, and a valveyoke surrounding the valve stem, the system comprising:first strainsensor means secured to the valve yoke and substantially parallel to thevalve stem for sensing strains experienced by the valve yoke which areproportional to the forces on the valve yoke and are equal and oppositeto the forces on the valve stem, the first strain sensor means also forgenerating electrical signals proportional to the forces on the valvestem; second strain sensor means secured to the valve operator forsensing strains experienced by the valve operator and for generatingelectrical signals proportional to forces on the valve operator; torqueand limit switch indicating means for detecting the state of the torqueand limit switches and for generating electrical signals; and displaymeans electrically connected to the first and second strain sensor meansand to the torque and limit switch indicating means for receiving thegenerated electrical signals and for indicating the forces on the valvestem, the forces on the valve operator and the opening and closing ofthe torque and limit switches to permit identification of a disruptionin normal valve and/or valve operator functioning.
 10. A device formeasuring and indicating the forces on a valve stem of a valve having anoperator within an operator housing, over at least a portion of thevalve stroke, the device comprising:first strain sensor means secured toa valve yoke and substantially parallel to the valve stem for sensingstrains experienced by the valve yoke, which are proportional to theforces on the valve yoke and are equal and opposite to the forces on thevalve stem, the first strain sensor means for generating firstelectrical signals proportional to the forces on the valve stem;vibration measuring means on a surface of the valve operator for sensingvibrations in the valve and/or valve operator and for generating secondelectrical signals proportional thereto; and display means electricallyconnected to the first strain sensor means and to the vibrationmeasuring means for receiving the first and second electrical signalsand for indicating the forces on the valve stem and the vibrationsoccurring in the valve and/or valve operator.
 11. A device for measuringand indicating the forces on a valve stem of a valve having an operatorwithin an operator housing, over at least a portion of the valve stroke,the device comprising:first strain sensor means secured to a valve yokeand substantially parallel to the valve stem for sensing strainsexperienced by the valve yoke which are proportional to the forces onthe valve yoke and are equal and opposite to the forces on the valvestem, the first strain sensor means for generating first electricalsignals proportional to the forces n the valve stem; second strainsensor means secured to the valve operator housing for sensing strainsexperienced by the operator housing, the second strain sensor means forgenerating second electrical signals proportional to forces on theoperator housing; vibration measuring means on a surface of the valveoperator for sensing vibrations in the valve and/or valve operator andfor generating third electrical signals proportional thereto; anddisplay means electrically connected to the first and second strainsensor means and to the vibration measuring means for receiving thefirst, second and third electrical signals and for indicating the forceson the valve stem and on the operator housing and vibrations occurringin the valve and/or valve operator.
 12. A system for evaluating thecondition and performance of a valve and valve operator combination,including a valve, a valve operator containing a motor, gearing, aspring pack and torque and limit switches, a valve stem extendingbetween the valve operator and the valve, and a valve yoke surroundingthe valve stem, the system comprising:first strain sensor means securedto the valve yoke and substantially parallel to the valve stem forsensing strains experienced by the valve yoke which are proportional tothe forces on the valve yoke and are equal and opposite to the forces onthe valve stem, the first strain sensor means for generating firstelectrical signals proportional to the forces on the valve stem;vibration measuring means on a surface of the valve operator for sensingvibrations in the valve and/or valve operator and for generating secondelectrical signals proportional thereto; valve stem motion sensor meansfor detecting motion and direction of movement of the valve stem and forgenerating electrical signals proportional to the velocity of valve stemmovement, the signals having a polarity indicative of the direction ofvalve stem movement; and display means electrically connected to thefirst strain sensor means, the vibration measuring means and to thevalve stem motion sensor means for receiving the first and secondelectrical signals and the valve stem movement signals and forindicating the forces on the valve stem, the vibrations occurring in thevalve and/or valve operator and the corresponding valve stem velocity topermit identification of a disruption in normal valve and/or valveoperator functioning.
 13. A system for evaluating the condition andperformance of a valve and valve operator combination, including avalve, a valve operator containing a motor, gearing, a spring pack andtorque and limit switches, a valve stem extending between the valveoperator and the valve, and a valve yoke surrounding the valve stem, thesystem, comprising:first strain sensor means secured to the valve yokeand substantially parallel to the valve stem for sensing strainsexperienced by the valve yoke which are proportional to the forces onthe valve yoke and are equal and opposite to the forces on the valvestem, the first strain sensor means for generating first electricalsignals proportional to the forces on the valve stem; vibrationmeasuring means on a surface of the valve operator for sensingvibrations in the valve and/or valve operator and for generating secondelectrical signals proportional thereto; spring pack motion sensor meansfor detecting motion and direction of movement of the spring pack andfor generating electrical signals proportional to the velocity of springpack movement, the signals having a polarity indicative of the directionof spring pack movement; and display means electrically connected to thefirst strain sensor means and to the vibration measuring means forreceiving the first and second electrical signals and connected to thespring pack motion sensor means for receiving the generated electricalsignals, the display means for indicating the forces on the valve stemand the vibrations occurring in the valve and/or valve operator and thecorresponding spring pack velocity to permit identification of adisruption in normal valve and/or valve operator function.
 14. A systemfor evaluating the condition and performance of a valve and valveoperator combination, including a valve, a valve operator containing amotor, gearing, a spring pack and torque and limit switches, a valvestem extending between the valve operator and the valve, and a valveyoke surrounding the valve stem, the system comprising:first strainsensor means secured to the valve yoke and substantially parallel to thevalve stem for sensing strains experienced by the valve yoke which areproportional to the forces on the valve yoke and are equal and oppositeto the forces on the valve stem, the first strain sensor means forgenerating first electrical signals proportional to the forces on thevalve stem; vibration measuring means on a surface of the valve operatorfor sensing vibrations in the valve and/or valve operator and forgenerating second electrical signals proportional thereto; motor currentsensor means for detecting the flow of current through the motor and forgenerating electrical signals proportional to the motor current; anddisplay means electrically connected to the first strain sensor means,to the vibration measuring means and to the motor current sensor meansfor receiving the first and second electrical signals and the signalsgenerated by the motor current sensor means and for indicating theforces on the valve stem, the vibrations occurring in the valve and/orvalve operator and the corresponding motor current to permitidentification of a disruption in normal valve and/or valve operatorfunctioning.
 15. A system for evaluating the condition and performanceof a valve and valve operator combination, including a valve, a valveoperator containing a motor, gearing, a spring pack and torque and limitswitches, a valve stem extending between the valve operator and thevalve, and a valve yoke surrounding the valve stem, the systemcomprising:first strain sensor means secured to the valve yoke andsubstantially parallel to the valve stem for sensing strains experiencedby the valve yoke which are proportional to the forces on the valve yokeand are equal and opposite to the forces on the valve stem, the firststrain sensor means for generating first electrical signals proportionalto the forces on the valve stem; vibration measuring means on a surfaceof the valve operator for sensing vibrations in the valve and/or valveoperator and for generating second electrical signals proportionalthereto; torque and limit switch indicating means for detecting thestate of the torque and limit switches and for generating electricalsignals; and display means electrically connected to the first strainsensor means, to the vibration measuring means and to the torque andlimit switch indicating means for receiving the first and secondelectrical signals and the electrical signals generated by the torqueand limit switch indicating means and for indicating the forces on thevalve stem, the vibrations occurring in the valve and/or the valveoperator and the corresponding opening and closing of the torque andlimit switches to permit identification of a disruption in normal valveand/or valve operator functioning.